The primary objective of the proposed research is to study single and fractionated therapies of low LET radiation and/or selected drugs using 9L spheroids. Homogeneous spheroids will be obtained by screening spinner cultures and will be treated either in bulk spinner culture or individually in agar-lined multitest wells. Spheroids will be analyzed for cell kill, growth delay, histological changes, and recovery kinetics. An in depth study of a relatively few agents should detect those experimental parameters relevant to the observed cytotoxic effects. This approach should provide basic knowledge of the biological responses of tumor cells to treatment and suggest logical therapeutic strategies for in vivo application.